Purchase this article with an account.
A. Ho, F. Manns, S. Evans, G. Brent; Third–order Theory Analysis of the Spherical Aberration of Pseudo–accommodating IOLs . Invest. Ophthalmol. Vis. Sci. 2005;46(13):819.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Pseudo–accommodating IOLs (P–IOL) are now available for supplementing near vision following cataract extraction. With the possible integration of aberration–correction technology (e.g. wavefront–guided LASIK) with P–IOL, study of the aberrations of P–IOL is relevant. We used third–order theory to analyse the spherical aberration (SA) of P–IOL and to identify issues relating to their optimisation. Methods: A modified Navarro eye model was used. An 18D P–IOL was modelled at a pupil size of 5 mm. To simplify calculations, the refractive index of the vitreous and aqueous was assumed to be the same. Two conjugate ratios were considered representing distance viewing (at infinity) and near viewing at 1 m. The coefficients (W040) for the SA contribution of each ocular surface were computed for both conjugate factors. The lens bending factor (BF) to achieve minimal SA for bi–spherical surface P–IOL was computed for distance and near viewing either including or excluding the contributions of the ocular component, with a range of P–IOL refractive indices (n). The asphericity required to eliminate SA for each of the four previous scenarios was also computed. Results: The axial shift required to achieve 1D was 0.897 mm. The total SA contribution of the ocular components was 1.42 µm at distance and 1.51 µm at near SA cannot be eliminated for distance or near using only spherical P–IOL surfaces. In general, SA is minimised with the more convex surface of P–IOL leading (i.e. BF>0). SA of optimised spherical P–IOL decreases as n increases (e.g. 2.33 µm when BF=0.405, n=1.40, and 0.325 µm when BF=1.081, n=1.50). When n=1.488, a convex–plano design is optimum giving a P–IOL SA of 0.38 µm at distance. To eliminate the SA of P–IOL only, front surface must be hyperbolic for n<1.402 and prolate ellipse for greater n. Due to its flatter surface, back surface must be highly hyperbolic to eliminate SA. To eliminate SA of the eye and P–IOL combined, extremely hyperbolic aspheres are required regardless of front or back surface Conclusions: Considerations of third–order theory provides useful insight towards optimisation of P–IOLs. Unlike the natural human eye, SA becomes more positive during near vision with all designs of P–IOL.
This PDF is available to Subscribers Only